Expand Configuration and Management Manual (G06.24+)

Troubleshooting
Expand Configuration and Management Manual—523347-008
21-38
Adding Low-Speed Lines to a Multi-Line Path
Adding Low-Speed Lines to a Multi-Line Path
Adding more low-speed lines to a multi-line path can increase the number of OOS
frames that a path needs in order to reassemble. The effect in this case is not on the
buffer space used but on the total time taken for the sending Expand line-handler
process to receive its ACK. As a result, the sending node may experience an increase
in Layer 4 timeouts. The solution to this problem is to reconfigure the Expand line-
handler process to have larger Layer 4 timeout (L4TIMEOUT modifier) and OOS
timeout (OSTIMEOUT modifier) values.
Duplicate Node
The Expand subsystem identifies nodes primarily by their node (system) number. For
any single network, each node must have a unique number in the range 0 through 254.
It is possible to introduce a node into a network with a configured node number that is
the same as that of a node that already exists in the network. The results of such a
mistake vary depending on the network topology, but can be characterized by a few
general symptoms, as described below:
•
Applications that previously succeeded begin to fail with file-system error 201. All
failing applications are attempting to access the same destination node.
•
The number of NCPM packets increases steadily. NCPM packets can be observed
by issuing an Expand subsystem SCF STATS PATH command.
•
When an SCF INFO PROCESS $NCP, NETMAP command is issued, connections
repeatedly alternate between connected and disconnected states.
The effect of a duplicate node number on user applications depends on the network
topology and, in particular, on the size of the network. Those nodes closer (in terms of
the routing algorithm) to the erroneously numbered node than to the correctly
numbered node regard the invalid node as a better route and alter their routing tables
and connect to the invalid node. Applications that were communicating with the valid
node are not able to continue and may receive file-system error 201.
To resolve a duplicate node name and/or number problem, refer to Changing System
Names and Numbers on page 19-22.
Note. The multi-line path does not need to be attached to the sending node. In a multiple-hop
circuit, the problem may be caused by a multi-line path on the receiving node.
Note. Any one of the symptoms described above may be caused by factors other than a
duplicate node in the network. However, the presence of all symptoms and their persistence is
a good indication that a duplicate node number has been introduced.